The experiments in this application are designed to test the hypothesis that: 1. Cyclin C associates with proteins involved in cell cycle control including novel cdk's, "pocket proteins" such as p130, and as yet undefined proteins; and 2. Cyclin C's associations with these proteins help govern cell cycle progression. To test these hypotheses, it is proposed to: (a) identify cyclin C associated proteins; (b) examine cyclin C's association with p130; and (c) test activities of cyclin C associated proteins.